Twisted

One day Prof Clipper, a renowned physicist, got locked out of his office. A student accompanying him offered to fetch the duplicate key, but the Prof gestured otherwise. He searched his pockets and brought out a couple of twisted paper-clips. Next he inserted them in the lock and fiddled with the lock. There was a click and the lock opened.

The student was amazed and asked – How many paper-clips did you use to make that lock-pick?